This invention relates generally to the field of elastomer plastics blends or blends of polyolefin plastics with olefinic elastomers, mineral and/or carbon black fillers and, optionally, hydrocarbon process oil, process aids, etc. Specifically, it is directed to blends of polyolefin plastics such as polypropylene, polypropylene reactor copolymer, polybutylene, linear low density polyethylene, and high density polyethylene with a copolymer of ethylene, olefinic elastomer, mineral and/or carbon black filler, and, optionally, hydrocarbon process oil, process aids, polymer-filler coupling agents, antiblock additives, antioxidants, pigments, foaming agents, etc. More specifically, it is directed to compositions comprising blends of polypropylene, ethylene-propylene copolymer or terpolymer elastomer, ethylene-vinyl acetate copolymer and mineral filler, e.g., alumina trihydrate. The compositions can be used as insulation on wire for low voltage applications without the necessity for vulcanization. The compositions exhibit good retention of properties after heat aging and, where the appropriate mineral filler is used, excellent flame retardant properties.
Blends similar to those described herein are disclosed in copending U.S. patent application Ser. No. 362,103, filed Mar. 26, 1982. The similarities relate primarily to the polymeric components, however, polyethylene is not specifically recommended for use in the blends herein. Furthermore, the blend compositions disclosed and claimed herein utilize mineral and/or carbon black fillers as an integral part of the composition and treat hydrocarbon process oil as an optional ingredient. In a significant point of departure, the invention disclosed herein is an insulated, electrically conductive substrate wherein the blend composition is employed as the insulating member; the reference did not recognize that similar blends could be developed which would have the advantageous and useful properties and uses disclosed herein. The disclosure of U.S. patent application Ser. No. 362,103 is incorporated herein by reference.
It is well known that a polyolefin such as polyethylene can be employed by itself or in blends with other polymers to produce electrically insulating compositions. However, such compositions are typically vulcanized, see, e.g., U.S. Pat. No. 3,433,891 and U.S. Pat. No. 4,322,575. The compositions disclosed in these prior art references are not thermoplastic since they are vulcanized compositions. Furthermore, they fail to describe the particular blend of ingredients taught herein, the latter resulting in the advantageous structures disclosed.
U.S. Pat. No. 4,303,571 teaches the preparation of a film forming blend composition comprising ethylene-propylene elastomers, ethylene-vinyl acetate copolymers and a hydrocarbon oil plasticizer. However, the reference does not recognize that such a composition can be advantageously blended with polyolefin plastics nor, that mineral and/or carbon black fillers are required and that the compositions are specifically useful as electrical insulation.
Compositional differences also distinguish the instant invention from other references disclosing thermoplastic elastomer compositions, for example Japanese Kokai to Sumitomo Chemical, No. 77 126,450 and Japanese Kokai to Mitsui Petrochemical, No. 80 71, 739. The former reference discloses a modified copolymer rubber composition for use in extruded and molded articles. Additionally, the compositions of the latter reference are intended to be treated with a peroxide crosslinking agent.